1. Field of the Invention
The present invention relates to an electronic camera that captures a subject image with an image-capturing device.
2. Description of the Related Art
An apex operation is performed to determine the correct exposure quantity in a camera in the related art through the following formula (1) by using the aperture value AV of the photographic lens, the shutter speed (exposure time length) TV, the subject brightness BV and the exposure sensitivity SV.EV=AV+TV=BV+SV  (1)EV in the expression above represents the exposure quantity.In a silver halide camera, SV is determined by the sensitivity of the film being used in the camera and, accordingly, the aperture value AV and the shutter speed TV are calculated in correspondence to the subject brightness BV. If the exposure sensitivity SV of the image-capturing device can be varied in an electronic camera, the aperture value AV, the shutter speed TV and the exposure sensitivity SV are calculated in correspondence the subject brightness BV.
Under normal circumstances, if the exposure sensitivity SV is raised in an electronic camera, the noise that is superimposed on image signals increases to result in poor image quality. Accordingly, it is desirable to set an upper limit for the exposure sensitivity SV to ensure that the S/N ratio of the image does not fall below a specific value in an exposure sensitivity change mode which allows the exposure sensitivity SV to be varied. At the same time, a higher priority should be given to achieving the correct exposure than achieving a better S/N ratio for the image in a situation in which full exposure cannot be achieved easily, e.g., during a photographing operation performed in a dark area or during a photographing operation that needs to be performed at a higher shutter speed TV. In order to address this need, an electronic camera that can be set in a sensitivity boost mode in which the exposure sensitivity SV can be set higher than the upper limit has been proposed in the known art. Since the upper limit is set to the exposure sensitivity SV in the exposure sensitivity change mode and the exposure sensitivity SV can be set higher than the upper limit in the sensitivity boost mode, an operational conflict occurs if the two modes are set at the same time.
In addition, the subject brightness BV is often low in a situation that necessitates the use of an electronic flash unit for illuminating the subject. Under normal circumstances, the image-capturing sensitivity SV is adjusted to a higher value in the exposure calculation executed by using formula (1) above if the subject brightness BV is low. In such a case, there is a risk of an increased noise in the image signals to result in degraded image quality and, for this reason, it is better not to change the image-capturing sensitivity. In addition, if no photographic lens is mounted at the electronic camera, lens information such as the aperture value AV necessary for the exposure calculation is not available to the camera, and thus, the image-capturing sensitivity SV cannot be determined accurately. When the full information necessary for the exposure calculation is not available as described above, it is better not to change the image-capturing sensitivity SV that has been set.